1. Field of the Invention
The present invention relates to LC-included electronic components, and in particular, to an LC-included electronic component for use in a high frequency band.
2. Description of the Related Art
A conventional laminated LC filter is shown in FIGS. 10 and 11. As shown in FIG. 10, a laminated LC filter 1 includes ceramic sheets 2 to 8 each having a plurality of inductor via holes 10a to 10d, 11a to 11d, and 12a to 12d, resonant capacitor patterns 13 to 15, coupling capacitor patterns 19 to 26, input/output lead patterns 30 and 31, and shield patterns 28 and 29.
The laminated unit 34 shown in FIG. 11 is obtained by stacking the ceramic sheets 2 to 8 in the Z direction, covering the top and bottom surfaces of the sheets with protecting ceramic sheets, and monolithically burning the ceramic sheets. An input terminal P1, an output terminal P2, and ground terminals G1 and G2 are provided on the laminated unit 34. The input/output lead pattern 30 is connected to the input terminal P1, and the input/output lead pattern 31 is connected to the output terminal P2. Ends of the shield patterns 28 and 29 are connected to the ground terminal G1 and the other ends of the shield patterns 28 and 29 are connected to the ground terminal G2.
In the above-described LC filter 1, the inductor via holes 10a to 10d, 11a to 10d, and 12a to 12d, which are arranged in the X direction in FIG. 10, are successively connected to one another in a direction in which the ceramic sheets are stacked, defining columnar inductors L1, L2, and L3. The resonant capacitor patterns 13, 14, and 15 are opposed to the shield pattern 29, with the ceramic sheets 6 and 7 provided therebetween, defining resonant capacitors C1, C2, and C3, respectively. Accordingly, the columnar inductor L1 and the capacitor C1 define an LC resonator Q1, the columnar inductor L2 and the capacitor C2 define an LC resonator Q2, and the columnar inductor L3 and the capacitor C3 define an LC resonator Q3.
In general, filter characteristics of an LC filter are subject to resonator Q. The Q of the resonator is primarily determined by the Q of an inductor. The Q of the inductor is subject to a loss (resistance) of the inductor. Accordingly, to increase Q of the LC resonators Q1 to Q3 which define the LC filter 1, the section areas on the X-Y plane of the columnar inductors L1 to L3 formed by successively connecting the via holes must be increased. However, since the conventional columnar inductors L1 to L3 have circular section shapes, the increased section areas narrow the intervals of the columnar inductors L1 to L3, which are adjacent, and generate excessively strong inductive coupling. Therefore, to obtain the desired inductive coupling, the intervals of the columnar inductors L1 to L3 must be substantially widened, which results in a substantially increased product size.
In When the via holes 10a to 12d having section areas are provided on the ceramic sheets 2 to 5 to increase Q, cracks often occur in the laminated unit 34 when it is burned, due to the difference in thermal contraction between conductive material of the via holes 10a to 12d and insulating material of the ceramic sheets 2 to 5. Thus, the section areas of the via holes 10a to 12d cannot be sufficiently increased.
To overcome the above-described problems with the prior art, preferred embodiments of the present invention provide a small-sized LC-included electronic component having an increased Q of a resonator and having outstanding reliability.
An LC-included component according to a preferred embodiment of the present invention includes an LC resonator having at least one inductor and at least one capacitor. The at least one inductor and the at least one capacitor are provided in a laminated unit defined by stacked insulating layers. The inductor is defined by via holes successively connected in a stack direction in which the insulating layers are stacked. In the section shape of each of the via holes on an X-Y plane perpendicular to the stack direction, a dimension in the X direction differs from a dimension in the Y direction.
By differentiating the X dimension and Y dimension of each via hole, a desired balanced inductive coupling and resonator Q are achieved, even when the section area of each via hole is increased.
In addition, by arranging the Y-direction ends of the section shape of each via hole defining the inductor to have a relatively large width, current concentration at each longitudinal end of each via hole due to the edge effect of high frequency current is reduced.